Known composite materials include fiberglass continuous tows that are thoroughly impregnated with thermoplastic resins. The resulting composite typically has a cross-sectional area ratio of glass to resin of 0.50 or more. The composite is high in strength and low in elongation, but poor in flexibility so that it sometimes has problems with handling and post-processing.
Resin coated fiberglass strands are known for making scrim useful, for instance, for window screens. They have a large proportion of glass fibers and a small proportion of resin that coats the periphery of the glass fiber bundle. When combined with a large volume percentage of glass, resin/glass composites are stable under a variety of moisture and temperature conditions encountered during normal seasonal weather conditions.
There are also certain thermoplastic resins, such as polypropylene, that are inherently stable under a variety of moisture conditions, but which are not always preferred for wear, strength, aesthetic, or other reasons. Other thermoplastic resins, such as polyimides and polyamides, are dimensionally sensitive to moisture and temperature, with moisture sensitivity predominating. Nylon is one such resin that may absorb up to about 8.5% moisture and undergo significant dimensional changes from maximum expansion to maximum shrinkage of 3% or more. It has been found in the case of a nylon/fiberglass composite strand material, with a large proportion of nylon, that poor dimensional stability may occur when the strand expands at high humidity and shrinks at low humidity. Temperature affects the amount of expansion or shrinkage for a given humidity condition.
There is a need for a strand material that can be made using a high proportion of moisture sensitive resin, preferably nylon, that is stable when exposed to extremes of moisture and temperature periodically encountered in the environment, such as low humidity at both high and low temperatures, and high humidity at both high and low temperatures.
There is a need for a stable, flexible strand that can be used as an adhesive and structural component in a composite assembly, such as a carpet assembly, which incorporates an elongated pile article made from a strand as described in copending U.S. patent application Ser. No. 08/017,162, filed Feb. 22, 1993 by the assignee of the present invention, the disclosure of which is hereby incorporated by reference. In such a use, the strand must have a large proportion of resin (nylon) for it to be ultrasonically bondable with the preferred nylon carpet yarn. When incorporated in a carpet assembly, which may also use the ultrasonic bonding techniques, the coating of the resin must remain around the reinforcing filaments to protect the filaments, and the strand must be flexible and strong during processing and assembly into the carpet. The strand must also resist moisture and thermal expansion forces developed in the nylon of the strand so buckling will not occur in the carpet assembly under normal conditions of temperature and humidity changes.